1. Field of the Invention
The present invention relates to a focus control system for photographic apparatus, in general, and to a simplified focus control system for positioning a supplemental lens into and out of the optical path of a fixed focus lens in such apparatus, in particular.
2. Description of the Prior Art
Systems in which the objective lens of a camera may be automatically focused on a subject are well known in the prior art. In commonly owned U.S. Pat. No. 4,357,083 to Johnson et al., for example, a method and apparatus are disclosed wherein means are provided for actuating a light source to thereby illuminate a scene to be photographed with artificial illumination. Light sensing means including a photodetector are employed to provide a range signal responsive to the intensity of reflected radiation which may then be employed to adjust the focus of a variable focus lens, for image focusing purposes.
In commonly owned U.S. Pat. No. 4,148,574 to Johnson, a focusing system for a photographic camera employs ultrasonic energy for focusing a single adjustable focus lens having two focal positions. Ultrasonic energy is transmitted toward a subject to be photographed and the reflection of such energy from the subject is subsequently detected. Characteristics including the time duration between ultrasonic energy transmission and detection are electronically processed to develop a control signal representative of the distance between the subject and the camera. The control signal is then used to select one of the two focal positions of the two focal position lens that will focus the sharpest image of the subject to be photographed at the focal plane of the camera.
In commonly owned U.S. Pat. No. 4,336,988 to Johnson, a lens focusing system for a photographic camera which includes a plurality of discrete lens elements, wherein each of the lens elements has a different focal length, is disclosed. The lens elements are mounted in a circumferentially spaced-apart relation on a rotatably mounted lens disc for rotation about a disc center axis. The lens focusing system further includes an ultrasonic ranging system for measuring the photographic camera-to-subject distance and for deriving a signal representative thereof. A combination of a lens disc drive coupled to the lens carrying disc and a disc stopping pawl, responsive to the camera-to-subject distance signal, stop the rotating lens disc and thereby locate a lens element in an optical axis of the camera that will form the sharpest image at the camera's focal plane.
While the above-described lens focusing systems have achieved various degrees of success, they generally utilize large numbers of components which make such lens focusing systems relatively large and complex for optimum camera packaging purposes and/or relative costly to economically produce.